feat: Phase 2 — ports package, secrets port move, postgres adapter move

Problem: the hexagon's Phase 2 (plans/2026-08-15-hexagonal-architecture.md)
must give the use-cases-to-be their contract surface: driven-port
interfaces, test fakes, the secrets interface moved into core, and the
postgres package inside the adapters tree — before the first vertical
slice (Phase 3) can wire a composition root.

Change:
- internal/core/ports: full driven-port catalog per plan §3.3 —
  repositories as transaction-scoped aggregates whose inputs carry
  derived checks, audit, and events (§3.6), plus CommandExecutor,
  TargetResolver, Checker, Secrets, EventPublisher, Provisioner.
  Port-local payload types (Event, AuditEntry, CheckDef, KnowledgeEntry,
  ExecResult) keep signatures off infrastructure; TypeTree aliases
  internal/ontology (pure over domain) until checkdefaults is absorbed.
  ReadModels intentionally not declared yet — it materializes with the
  Phase 3 slice and grows as report handlers rewire.
- secrets.Backend is now an alias of ports.Secrets; implementations
  (Infisical, SOPS, Manager) unchanged. mcp's local secretBackend
  subset is deleted; tool constructors take ports.Secrets.
- internal/db → internal/adapters/postgres (mechanical import rewrite;
  package identifier stays db until the Phase 3 repository split).
  sqlc.yaml, Makefile, golangci exclusions, and docs follow the move;
  make generate-check verified.
- internal/adapters/ssh: Executor implements ports.CommandExecutor over
  the actuator dial pool + RunStreaming (10-min default timeout carried
  over from the httpapi path).
- internal/adapters/remote: Resolver implements ports.TargetResolver
  delegating to internal/remote (still pool-based; drops onto
  ports.EntityRepository when repositories land in Phase 3 — documented
  transitional import).
- internal/core/ports/portstest: importable fakes — in-memory
  EntityRepo (with check-then-act SetState, side-effect recording),
  RecordingExecutor, FakeChecker, SpyPublisher; port-satisfaction
  guards; tests.

Risk: ports are declared ahead of implementations — signatures firm up
per phase as slices land (documented in the package doc); the
remote→postgres transitional import is explicit and dissolves in
Phase 3.

Verification: go vet, make test (race, 19 packages), generate-check,
golangci on core+adapters — 0 issues; full-repo baseline down
365→344.

internal/adapters/ssh/executor.go

@@ -0,0 +1,114 @@
+// Package ssh implements ports.CommandExecutor over internal/actuator:
+// the dial pool, host-key handling, and streaming/combined execution.
+package ssh
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+	"os"
+	"sync"
+	"time"
+
+	cryptossh "golang.org/x/crypto/ssh"
+
+	"github.com/dtoro/oikos/internal/actuator"
+	"github.com/dtoro/oikos/internal/core/ports"
+)
+
+const (
+	defaultExecTimeout = 10 * time.Minute
+	defaultKeyPathEnv  = "OIKOS_SSH_KEY_PATH"
+	defaultKeyPath     = "/etc/oikos/ssh_key"
+)
+
+// SignerSource supplies the SSH signer used for all dials. The secrets
+// adapter provides one backed by Infisical/SOPS; tests inject a static one.
+type SignerSource func(ctx context.Context) (cryptossh.Signer, error)
+
+// FileSignerSource reads an OpenSSH private key from disk once and parses
+// it (path from env OIKOS_SSH_KEY_PATH, default /etc/oikos/ssh_key — the
+// same resolution the httpapi path used before the extraction).
+func FileSignerSource() SignerSource {
+	var (
+		once   sync.Once
+		signer cryptossh.Signer
+		err    error
+	)
+	return func(context.Context) (cryptossh.Signer, error) {
+		once.Do(func() {
+			path := os.Getenv(defaultKeyPathEnv)
+			if path == "" {
+				path = defaultKeyPath
+			}
+			key, rerr := os.ReadFile(path)
+			if rerr != nil {
+				err = fmt.Errorf("read ssh key %s: %w", path, rerr)
+				return
+			}
+			signer, err = actuator.LoadSignerFromBytes(key)
+		})
+		return signer, err
+	}
+}
+
+// Executor runs commands over SSH through a dial pool.
+type Executor struct {
+	signer SignerSource
+	pool   *actuator.DialPool
+}
+
+var _ ports.CommandExecutor = (*Executor)(nil)
+
+// NewExecutor builds an executor. The dial pool reuses connections per
+// host/user for the given TTL.
+func NewExecutor(signer SignerSource, poolTTL time.Duration) *Executor {
+	return &Executor{
+		signer: signer,
+		pool:   actuator.NewDialPool(poolTTL),
+	}
+}
+
+// Close releases pooled connections.
+func (e *Executor) Close() { e.pool.Close() }
+
+// Run dials the target (via the pool), wraps the command for transport when
+// the target needs it (pct/qm guests), executes with streaming output, and
+// maps the outcome onto ports.ExecResult.
+func (e *Executor) Run(ctx context.Context, target ports.Target, command string, opts ports.ExecOpts) ports.ExecResult {
+	start := time.Now()
+
+	signer, err := e.signer(ctx)
+	if err != nil {
+		return ports.ExecResult{Err: err, Duration: time.Since(start)}
+	}
+
+	client, err := e.pool.Get(ctx, actuator.DialOptions{
+		Host:   target.Host,
+		User:   target.User,
+		Signer: signer,
+	})
+	if err != nil {
+		return ports.ExecResult{Err: err, Duration: time.Since(start)}
+	}
+	// Pooled client: do not close here; the pool evicts on TTL.
+
+	if target.Wrap != nil {
+		command = target.Wrap(command)
+	}
+
+	timeout := opts.Timeout
+	if timeout <= 0 {
+		timeout = defaultExecTimeout
+	}
+
+	output, runErr := actuator.RunStreaming(ctx, client, command, opts.Sink, timeout)
+	if runErr != nil {
+		slog.Debug("ssh exec: command failed", "host", target.Host, "error", runErr)
+	}
+	return ports.ExecResult{
+		Output:   output,
+		Duration: time.Since(start),
+		Err:      runErr,
+	}
+}